Faculty Publications
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Item Factors influencing streambed hydraulic conductivity and their implications on stream–aquifer interaction: a conceptual review(Springer Verlag service@springer.de, 2017) Naganna, S.R.; Deka, P.C.; Ch, S.; Hansen, W.F.The estimation and modeling of streambed hydraulic conductivity (K) is an emerging interest due to its connection to water quality, aquatic habitat, and groundwater recharge. Existing research has found ways to sample and measure K at specific sites and with laboratory tests. The challenge undertaken was to review progress, relevance, complexity in understanding and modeling via statistical and geostatistical approaches, literature gaps, and suggestions toward future needs. This article provides an overview of factors and processes influencing streambed hydraulic conductivity (K) and its role in the stream–aquifer interaction. During our synthesis, we discuss the influence of geological, hydrological, biological, and anthropogenic factors that lead to variability of streambed substrates. Literature examples document findings to specific sites that help to portray the role of streambed K and other interrelated factors in the modeling of hyporheic and groundwater flow systems. However, studies utilizing an integrated, comprehensive database are limited, restricting the ability of broader application and understanding. Examples of in situ and laboratory methods of estimating hydraulic conductivity suggest challenges in acquiring representative samples and comparing results, considering the anisotropy and heterogeneity of fluvial bed materials and geohydrological conditions. Arriving at realistic statistical and spatial inference based on field and lab data collected is challenging, considering the possible sediment sources, processes, and complexity. Recognizing that the K for a given particle size group includes several to many orders of magnitude, modeling of streambed K and groundwater interaction remain conceptual and experimental. Advanced geostatistical techniques offer a wide range of univariate or multi-variate interpolation procedures such as kriging and variogram analysis that can be applied to these complex systems. Research available from various studies has been instrumental in developing sampling options, recognizing the significance of fluvial dynamics, the potential for filtration, transfer, and storage of high-quality groundwater, and importance to aquatic habitat and refuge during extreme conditions. Efforts in the characterization of natural and anthropogenic conditions, substrate materials, sediment loading, colmation, and other details highlight the great complexity and perhaps need for a database to compile relevant data. The effects on streambed hydraulic conductivity due to anthropogenic disturbances (in-stream gravel mining, contaminant release, benthic activity, etc.) are the areas that still need focus. An interdisciplinary (hydro-geo-biological) approach may be necessary to characterize the magnitude and variability of streambed K and fluxes at local, regional scales. © 2017, Springer-Verlag GmbH Germany.Item Predictions of two popular closed-form models for unsaturated hydraulic conductivity (K) are compared with in situ measurements made in a sandy loam field soil. Whereas the Van Genuchten model estimates were very close to field measured values, the Brooks-Corey model predictions were higher by about one order of magnitude in the wetter range. Estimation of parameters of the Van Genuchten soil moisture characteristic (SMC) equation, however, involves the use of non-linear regression techniques. The Brooks-Corey SMC equation has the advantage of being amenable to application of linear regression techniques for estimation of its parameters from retention data. A conversion technique, whereby known Brooks-Corey model parameters may be converted into Van Genuchten model parameters, is formulated. The proposed conversion algorithm may be used to obtain the parameters of the preferred Van Genuchten model from in situ retention data, without the use of non-linear regression techniques.(Elsevier, Field evaluation of unsaturated hydraulic conductivity models and parameter estimation from retention data) Nandagiri, L.; Prasad, R.1996Item Effect of permeability of subsurface barrier on salt water intrusion in coastal aquifers(2006) Mahesha, A.; Lakshmikant, K.Semi-pervious, subsurface barriers are considered to be one of the viable solution for the control of saltwater intrusion in coastal aquifers. Investigations are carried out in this work to assess the performance of the barrier with different permeabilities using a finite element model. The advancement of saltwater - freshwater interface and the water table profiles are monitored for fresh water withdrawals at inland locations under the scenarios of wide ranging hydraulic conductivities of the barrier. The results indicated that barrier is able to check the advancement of the intrusion significantly with the hydraulic conductivity being less than certain limit. The performance of the barrier is also compared with no barrier conditions. Marked variations in the interface and water table profiles are observed as compared to no barrier condition. The performance of the barrier was not found to be satisfactory beyond certain limit of permeability.Item Hydraulic and compaction characteristics of leachate-contaminated lateritic soil(2007) Nayak, S.; Sunil, B.M.; Shrihari, S.Large quantities of leachate-contaminated lateritic soil results from dump yards in the southwest coast of India. These dump yards receive large quantities of municipal solid waste which includes chemical, industrial and biomedical wastes. Large areas of land are currently being used for this purpose. An extensive laboratory testing program was carried out to determine the compaction characteristics and hydraulic conductivity of clean and contaminated lateritic soil. Batch tests were used to study the immediate effect of leachate contamination on the properties of lateritic soil. Contaminated specimens were prepared by mixing the lateritic soil with leachate in the amount of 5%, 10% and 20% by weight to vary the degree of contamination. The results indicated a small reduction in maximum dry density and an increase in hydraulic conductivity due to leachate-contamination. The change induced by chemical reaction in the microstructure of the soil was studied by scanning electron microscope before and after contamination of soil with leachate. The structure of the leachate contaminated soil sample appeared to be aggregated in scanning electron microscope analysis. The aggregated structure increases the effective pore space and thus increases the hydraulic conductivity. Fifty percent increase in hydraulic conductivity was observed for specimens prepared at standard Proctor density and mixed with 20% leachate. Compaction characteristics did not change much with the presence of leachate up to 10%. With 20% leachate the maximum dry density decreased slightly indicating excess leachate in the soil. However the changes are not significant. © 2007 Elsevier B.V. All rights reserved.Item Interactions Between Soils and Laboratory Simulated Electrolyte Solution(2010) Nayak, S.; Sunil, B.M.; Shrihari, S.; Sivapullaiah, P.V.To study the impact of salt water intrusion on two types of soils from west coast region of India were investigated in the laboratory. The key characteristics evaluated included Atterberg limits, compaction characteristics, hydraulic conductivity and chemical characteristics of selected soils. The sea at this coast receives effluent from different points and hence the characteristics change with time and locality. Therefore, to maintain uniform composition, 0.5 N sodium chloride solution (NaCl) was prepared in the laboratory and batch tests were used to determine the immediate effect on soils. Soil specimens were prepared by mixing the soils with 0.5 N NaCl in the increments of 0, 5, 10 and 20% by weight to vary the degree of contamination. Experimental results of soils mixed with 0.5 N NaCl showed that the maximum dry density increases and the optimum moisture content (OMC) decreases with increasing sodium chloride concentration. The study also revealed that the hydraulic conductivity of the soils tested increases with increase in sodium chloride concentration. The Atterberg limits of contaminated specimens show a remarkable change when compared with uncontaminated specimens. © 2010 Springer Science+Business Media B.V.Item Geotechnical characteristics of lithomargic clay blended with marine clay as landfill liner material(CAFET INNOVA Technical Society cafetinnova@gmail.com 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2012) Allamaprabhu, K.; Sunil, B.M.; Nayak, S.; Fernandes, S.; Zafar, M.This paper reports a series of laboratory tests conducted on lithomargic clay (shedi soil), which is widespread over part of southwest coast of India, to assess whether it could be used as compacted clay liner for hydraulic barriers in engineered landfill. In order to assess the suitability of lithomarge as a barrier material, following tests such as index properties, compaction characteristics, hydraulic conductivity and unconfined compressive strength of the soil were conducted in the laboratory. From the studies, it is found that lithomargic soil is near to the recommended specifications for soils to be used as liner material. Suitable materials for soil liners are then obtained by blending different types of locally available soils to achieve the required low hydraulic conductivity and good strength. To achieve specifications for the liner material lithomargic clay is blended with 15% and 20% marine clay by weight of lithomargic clay. From standard compaction control, the blended soil shows hydraulic conductivity lower than the 1x10-7 cm/s. Acceptable zones (AZ) are constructed on the compaction plane to meet design objectives for hydraulic conductivity. It's strength properties show that the soil possesses higher strength than the recommended minimum strength of 200kPa, to support the overburden pressure imposed by the waste body. From the laboratory test results, it can be concluded that lithomargic clay blended with marine clay satisfies the requirements for a good soil liner material. © 2012 CAFET-INNOVA TECHNICAL SOCIETY.Item Effect of hydraulic conductivity on soil moisture uptake under saline conditions for wheat crop(2013) Devatha, C.P.; Ojha, C.S.P.; Hari Prasad, K.S.; Thalla, A.K.Salinity in soil can decrease plant available water and cause plant stress. The pattern of root water uptake for wheat was studied for saline as well as non-saline condition using non-linear root water uptake model. Experiments have been conducted using a salinity level of 4 dS/m and freshwater condition. The effect of salinity on soil moisture has been studied by varying the crop coefficient as well as hydraulic conductivity. The correction factor to the crop coefficient approach is found to be unsuccessful. However, the correction factor to the hydraulic conductivity for a non-saline condition improves the simulation of soil moisture uptake in case of saline soils. The exponential form of the equation is established for the hydraulic conductivity to soil moisture relationship under salinity level and freshwater sample. The present work also substantiates that the non-linearity parameter of root water uptake model (O-R model) is successful in simulation of soil moisture depletion in the crop root zone and does not vary more than 10% in case of saline soils. © 2013 Indian Society for Hydraulics.Item Semi Impervious Subsurface Barrier for Water Conservation in Lateritic Formations(Springer India sanjiv.goswami@springer.co.in, 2014) Udayakumar, G.; Mayya, S.G.The coastal districts of Karnataka in west coast of India experience acute shortage of drinking water during dry season in spite of heavy monsoon rains. Though sufficient recharge of ground water takes place, depletion of water table is very quick, once the rain recedes. It is mainly attributed to the presence of porous and highly permeable laterites and lateritic soils. The hydraulic conductivity of these soils varies in the range of 10?4 to 10?5 cm/s. The conventional water harvesting methods fail to solve the problem. It is necessary to explore innovative method to regulate the lateral subsurface flow and maintain a high water table over a prolonged period of time. The present work is an attempt to explore the possibility of using semi impervious Subsurface Barrier (SSB) to regulate and control the lateral flow of water in the unconfined aquifer in lateritic formations. Appropriate barrier material is arrived at using the locally available soil and the required properties are established. A SSB is built in a suitable location in an identified microwatershed using lateritic soil and the composite soil prepared by mixing requisite percentage of lateritic soil and clay. The hydraulic conductivity of these soils is maintained in the range of 10?6 to 10?7 cm/s so as to behave as semi impervious. The performance analysis is carried out by observing water levels in selected open observation wells before and after the construction of the barrier. The results have shown the successful performance of SSB in maintaining a high water table over a prolonged period of time during summer months, both in u/s and d/s of the barrier. © 2014, The Institution of Engineers (India).Item Assessment of soil moisture uptake under different salinity levels for paddy crop(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2016) Devatha, C.P.; Shankar, V.; Ojha, C.S.P.The core of salinity problems starts from the fact that irrigation waters contain some amount of dissolved salts. Soil moisture salinity is dependent on soil type, climate, water use, and irrigation. The root water-uptake pattern for paddies is studied for saline as well as nonsaline conditions in the present study using a nonlinear root water uptake model. Field crop experiments are carried out using irrigation water with two different levels of salinity (4 and 6.25 dS=m) and fresh water. The effect of salinity on soil moisture uptake is studied by two approaches, i.e., effect on crop coefficient and effect on hydraulic conductivity. Based upon the experimental observations for lowsaline (4 dS=m), high-saline (6.25 dS=m), and freshwater conditions, an exponential form of an equation is established for the hydraulic conductivity. The results obtained for soil moisture depletion in the crop root zone show significant improvement in prediction of soil moisture uptake for saline cases with the use of the obtained nonlinearity parameter. © 2016 American Society of Civil Engineers.Item Estimation of saturated hydraulic conductivity using fuzzy neural network in a semi-arid basin scale for murum soils of India(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2018) More, S.B.; Deka, P.C.Saturated hydraulic conductivity, Ks is an important input parameter in modeling flow process in soil. Measurement of Ks in field is time consuming and costly. Also, due to inherent temporal and spatial variability of this parameter, large number of samples are required to characterize the areas of site. In this study, a hybrid approach consists of Fuzzy Neural Network (FNN), has been proposed to estimate Ks from limited number of field measurements using Guelph permeameter. The various soil properties such as bulk density, porosity, specific gravity, sand, clay, silt and organic matter were used as input variables and Ks was kept as output. In this study, 175 field measurements and soil samples were collected in a grid of 40 m × 200 m with uniform spacing along the slope of barren land in the site of Punanaka (Solapur city), India. To quantify the prediction accuracy, this FNN approach is compared with regression, Fuzzy Mamdani approach and artificial neural network with BP algorithm. The various statistical performance indices like root mean square error, coefficient of determination (R2), and Mean relative error were used for evaluation of model performance. It was found that the hybrid FNN approach in comparison with others could more accurately predict saturated hydraulic conductivity. © 2017 Indian Society for Hydraulics.